1. Field of the Invention
The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus stably and efficiently supplying toner.
2. Discussion of the Related Art
Known image forming apparatuses, such as printers, facsimiles, copiers, and multifunction apparatuses that print, fax and copy, generally use an electrophotographic process for image forming. The electrophotographic process includes a process of charging an image carrier, a latent image forming process, a developing process in which color powder (toner) is adhered, and a transferring process that transfers the toner image to a recording medium, such as paper.
The known image forming apparatus includes an image carrier, a toner transporting member and a power supply. The toner is supplied to the toner transporting member using a magnetic brush, for example, and is then conveyed to the image carrier. The toner transporting member includes a plurality of electrodes arranged on a base member. The power supply supplies a multiple-phase AC voltage to the electrodes.
The plurality of electrodes is configured to generate a traveling-wave electric field to move the toner, and the multiple-phase AC (n-phase) voltages are applied to the electrodes of the transporting member to form a traveling-wave electric field in a direction toward the image carrier, so that the positively charged toner moves towards the image carrier. The toner is adhered to the image carrier to develop a latent image on the image carrier.
By this configuration, the toner is conveyed by the traveling-wave electric field to the image carrier. The developing speed is limited, however, by the amount of toner supplied to the toner transporting member. If the toner is supplied using a magnetic brush roller, the amount of toner supplied by the magnetic brush roller determines the developing speed.
If the toner cannot be conveyed due to an unsuitable voltage condition applied to the electrodes, the toner may adhere to the toner transporting member. Moreover, the electric field generated on the toner transporting member also affects the toner supply to the toner transporting member. This is a problem unique to the image forming apparatus that uses the traveling-wave electric field. If the electric field on the toner transporting member prevents the toner from being supplied to the toner transporting member, the efficiency of the development degrades due to the lack of toner.